Flavivirus infections, such as yellow fever, dengue (DEN), and Japanese encephalitis, represent a significant source of morbidity and mortality worldwide. DEN is a particular problem, due to the existence of four distinct virus serotypes. The barriers to the development of a successful DEN vaccine include lack of attenuated strains, and the occurrence of enhanced infection in type-specific immune individuals upon infection with a heterologous serotype. One potential approach to vaccine production, that obviates the need for use of the infectious organism, yet elicits the same type of immunity the organism does (often not the case with synthetic peptides or subunits), is the use of antiidiotype (anti-Id) antibodies, which represent the internal image of the original immunizing antigen. The goal of this project is the production of a cross-protective DEN anti-Id vaccine, based on the murine monoclonal antibody (MAb) 4G2, which has been shown to be directed against a cross-protective neutralizing epitope present on all flaviviruses. Production and testing of an anti-Id vaccine involves the following steps: (1) purification of MAb 4G2 (the idiotype); (2) immunization of mice with 4G2; (3) "capture" of the cells producing anti-4G2 antibodies (anti-Id) as hybridomas by cell fusion; and (4) use of purified anti-Id antibodies as immunogens, followed by-virus challenge of immunized animals. Phase 1 of.the project is currently underway, with the production of purified 4G2 antibody from ascites fluid of pristane-primed mice injected with the 4G2 hybridoma cell line. Because the hybridoma cell produces both a non-specific IgGl in addition to the anti-DEN IgG2a, Protein A (which binds IgG1 poorly), will be used as the first step in the purification scheme.